The present invention generally relates to an electrical casing and more particularly, to a shielding case for shielding a plurality of circuits such as high frequency circuits, local oscillation circuits, etc. from each other in a high frequency appliance, for example, an electronic tuner, a CATV (cable television) converter, or the like.
In a high frequency appliance dealing with frequencies higher than VHF or UHF band regions, a shielding case is employed to partition respective circuits for mutually shielding electronic circuits such as a high frequency amplification circuit, local oscillation circuit or the like.
Commonly, as shown in FIG. 10, the shielding case as described above is prepared by forming plate portions 101a to 101d for constituting an outer frame, and plate portions 101e to 101h for partitioning the frame interior on a single metallic flat plate through press work, and bending joint portions of the respective plate portions. As described above, by forming all the plate portions 101a to 101h on the single metallic plate, facilitation of the shielding case forming work and reduction in cost may be achieved.
In the known structure as described above, however, there is such a problem that, during formation of the shielding case as shown in FIGS. 11(A) and 11(B), when both the plate portions 101e and 101f are turned in a direction indicated by an arrow L after causing the plate portion 101f to erect on the plate 101e from the state of the flat plate, the end face of the plate portion 101f interferes with part of the plate portion 101a not folded as yet.
Accordingly, in order to avoid the interference as referred to above, it has been a conventional practice to form a notch 102 at the interfering portion of the plate portion 101a, or to provide notches 103 to 110 in the plate portions 101b to 101e as shown in FIG. 10, thereby to avoid the interference with the end faces of the other plate portions which are to be folded. As described above, in the conventional shielding case, the interference between the plate portions during the folding thereof has been avoided by preliminarily forming notches for facilitation of the shielding case manufacturing work.
However, in the known shielding case as described above, there is a disadvantage that, since part of each plate portion is chipped by the notches formed to avoid the interference between the plate portions during the folding thereof, shielding characteristic for the circuits tends to be deteriorated.